Vanishing Automobile update #17

How Dense Is Dense Enough?

How dense is dense enough for smart growth? Smart-growth advocates
in the Twin Cities (average density: 1,800 people per square mile)
say the Twin Cities needs to be as dense as Portland (average
density: 3,000 people per square mile).

Smart-growth advocates in Portland say that Portland needs
to be as dense as Los Angeles (average density: 5,600 per square
mile). Smart-growth advocates in Los Angeles say that Los Angeles
needs to be as dense as Chicago (average density: 12,000 people
per square mile).

Smart-growth advocates in Chicago say Chicago should be as
dense as San Francisco (average density: 16,000 people per square
mile). Smart-growth advocates in San Francisco want the City to
be even denser still. Where will it all end?

Fortunately for a puzzled nation, the Sierra Club answered
this question in a web page that supposedly calculates the environmental
impacts of density. You enter your preferred density in households
per acre along with your idea of average automobile fuel efficiency
(miles per gallon) and the price of gasoline. The Sierra Club
then projects the environmental and social impacts of your density.
For comparison, it includes the environmental and social impacts
of the "efficient urban density" and a "sprawl
density."

When originally posted on June 18, the web site indicated that
the efficient urban density is 500 households per
acre. Since the U.S. has an average of 2.4 people per household,
this represents 1,200 people per acre or 768,000 people per square
mile. This indicates that Manhattan, at only 52,000 people per
square mile, has a ways to go before it reaches smart-growth perfection.

Demographer Wendell
Cox points out that this is denser that the densest parts
of Mumbai (Bombay) and Hong Kong. In fact, Cox adds, at this density
everyone in the United States could fit into an area a little
larger than Portland, Oregon's urban-growth boundary.

Perhaps in response to Cox's comments, on June 20 the Sierra
Club modified the web page to compare four different densities:
* Dense urban, which is 400 households per acre
or slightly less than the "efficient urban" of the day
before;
* Efficient urban, which is "only" 100
households per acre;
* Efficient suburban, which is 10 households per
acre; and
* Sprawl, which the Sierra Club defines as one household
per acre.

Even the efficient urban density is incredibly dense compared
to what most people are used to. One hundred households per acre
is 153,600 people per square mile, or three times the density
of Manhattan. The "dense urban" 400 households per acre
is 614,400 people per square mile, or nearly twelve times as dense
as Manhattan.

Of course, 400 housing units could fit on an acre in a twenty-story
building, each story containing twenty apartments averaging a
little over 2,000 square feet. Add four or five more stories for
shops and offices and some underground parking and you have a
nice dense city of twenty-five-story buildings. But few cities
have large areas of twenty-five-story apartment/mixed-use buildings.
Even in Manhattan, most residences are in four- to ten-story buildings.

But the so-called efficient density of 100 households per acre
is scary enough. At that density, the population of the United
States could fit in the Los Angeles urbanized area -- call it
"Sierra Club City." The entire population of the world
would fit into the state of Virginia.

The Sierra Club assumes that all or nearly all office and retail
establishments would be mixed in with the residential areas. It
calculates that the efficient density would provide 48 "shopping
opportunities per acre," whatever that means, as opposed
to just 0.65 opportunities per acre at sprawl densities.

To be fair, some additional land would be needed for factories,
warehouses, and other industrial areas. But that would still leave
most of the rest of the world for farms, parks, and wilderness,
which of course is the Sierra Club's goal.

How much land would Sierra Club City save? At the present time,
U.S. cities, towns, and other urbanized areas occupy about 109,000
square miles of land. Roughly a third of that is industrial. If
Sierra Club City replaced the other two-thirds, that would allow
the restoration of about 72,000 square miles of land to farms,
forests, or nature preserves. That sounds like a lot, but it amounts
to just 2 percent of the land area of the United States.

Of course, if Sierra Club City stacks industry in twenty-five-story
buildings too, then up to 3 percent of the nation's land could
revert from urban uses to open space. Whether saving 2 or 3 percent
is worthwhile depends on the costs of high-density living.

Start with congestion. The Sierra Club says that people living
in sprawl densities of one household per acre would drive more
than 32,000 miles per year. But at the efficient densities, says
the club, they would drive only 7,600 miles per year, less than
a fourth as much. Of course, with 100 times as many people per
square mile, that means that total driving would be nearly 24
times more per square mile in Sierra Club City than in sprawl.

Urban Americans drive an average of 40,000 miles per square
mile of urbanized land each day. As the highest density urban
area, Los Angeles also has the highest density of driving: 124,000
miles per square mile of land.

But residents in the Sierra Club's efficient city would drive
1.3 million miles per day for each square mile of residential
area. That's 33 times more than in the average urban area and
10 times more than in Los Angeles.

Curiously, no matter what the population density, the Sierra
Club model dedicates 93 acres of land per square mile to roads
and sidewalks. It is not clear whether this is included in household
per acre densities or is in addition. Assuming that it is in addition,
then it represents about 13 percent of the land area, which is
about right for suburban areas but is far lower than the percentage
of high-density urban areas that is devoted to streets.

Ninety-three acres divided into twelve-foot lanes with three-foot
sidewalks represents about 50 lane-miles of roadway. To handle
1.3 million miles of vehicle travel per day, each lane-mile of
road would have to carry 1,100 vehicles per hour, twenty-four
hours a day, seven days a week. Non-freeway arterial lanes can
handle just that number, while freeway lanes can handle twice
this amount, and lesser streets (collectors and locals) do less.

Thus, Sierra Club City will be about as congested as Manhattan
during rush hour -- only congestion in Sierra Club city will be
24/7. The Sierra Club's "dense urban" density of 400
households per acre, of course, will be even worse: The club predicts
that people will drive more miles per lane mile than the best
freeways can handle.

With this much traffic concentrated in a small area, Sierra
Club City will be one of the most polluted cities in the history
of humanity. The city will produce less pollution per capita than
in a sprawling city, but it will be far more concentrated -- and
the health effects of automotive air pollution depend largely
on its concentration.

Typically, the Sierra Club model crudely assumes that pollution
is directly proportional to fuel consumption. The web site asks
you to enter the average fuel efficiency you imagine for your
city and it calculates the pounds of hydrocarbons (volatile organic
compounds), nitrogen oxides, particulates (PM10), and carbon dioxide
that will be produced. The Sierra Club doesn't estimate carbon
monoxide emissions, but autos tend to produce about ten times
as much CO as hydrocarbons.

The Sierra Club presents pollution in terms of pounds emitted
per household each year. For carbon dioxide, which is implicated
with global warming, total emissions may be crucial. But for many
of the other pollutants, the problem is not total emissions but
the concentration of emissions. Concentrations of carbon monoxide
and particulates, for example, pose extremely serious health risks,
while low levels can be tolerated and ignored by most people.

Sierra Club City will produce extremely dangerous levels of
these toxic pollutants. Based on the Sierra Club's numbers, automobiles
in sprawl emit about 100 pounds of hydrocarbons, a half ton of
carbon monoxide, and 680 tons of particulates per square mile
per day. But Sierra Club City will produce 2,340 pounds of hydrocarbons,
nearly 12 tons of carbon monoxide, and more than 16,000 pounds
of particulates per square mile per day.

Since the Sierra Club model assumes that emissions are proportional
to fuel consumption, all pollutants will be twenty-four times
as concentrated in Sierra Club City than in sprawl. But in fact,
cars pollute more in stop-and-go traffic, and the extra congestion
in Sierra Club City will make it even more polluted than the Sierra
Club numbers indicate.

The Sierra Club model also claims that high densities will
produce less water pollution. "When more than 20% of the
watershed is paved over and developed," says the club, "water
pollution skyrockets." But a suburban neighborhood of one
household per acre will have much less than 20 percent of its
area paved over, while an urban jungle of 100 households per acre
will be nearly all paved over. Thus, we can expect the most pollution
from the urban area.

The Sierra Club's model is optimistic about the effects of
density on driving. The model assumes that, at any density, doubling
density reduces per capita driving by 20 percent. This is about
four times greater than can be observed by looking at U.S. urban
areas. However, it is about the amount generated by studies that
looked at driving habits of residents of individual neighborhoods
of various densities.

The problem with such studies is that they usually fail to
control for family size, income level, and other factors that
influence driving. A disproportionate number of people in high-density
areas are either poor or have no children. They either can't afford
to drive or have decided they would prefer to use transit. But
this doesn't mean that forcing a middle-class family of four to
live in high densities will lead them to drive significantly less.

Even without this error, Sierra Club City -- a permanently
congested and dangerously polluted area -- will be far less attractive
to most Americans than sprawl. But smart-growth advocates will
nevertheless press for increasing densities in virtually every
U.S. city.

Supplemental Note

In response to the above report, the Sierra Club modified its
web site again to include the following statement:

The densities labeled 'efficient' provide transportation,
living, and work choices for residents and workers but do not
represent a Sierra Club endorsement of a specific density level.
That should ultimately be decided by the communities themselves.
The denser neighborhoods in Paris and Manhattan are shown for
comparison.

What does the Sierra Club mean by "communities"?
Communities don't make decisions; decisions are made by individuals.
It is most likely that the Sierra Club would like to see urban
planners and other appointed and elected officials made decisions
that everyone else will have to live with. That is what has happened
in Portland, Oregon, a city whose planning is endorsed by the
Sierra Club.

Rather than let city planners make decisions for other, the
Thoreau Institute's position is that densities should be decided
by the individuals living in those areas. That means initially
letting builders build for the market and letting individual homeowners
maintain their neighborhood densities through covenants protected
by small (perhaps 100 to 400 homes) neighborhood associations.